Error: There is no server in any of the selected server clusters [markloika: Development Cluster] that are eligible to start a new room in (they're all at full capacity or there are no servers in any of the clusters). Either change the selected clusters for your game in the admin panel, try again later or start some more servers for one of your clusters.
When I receive this error, there are no other clients connected to the dev server - so it's definitely not at full capacity.